Chemical Reactions and
Equations
Chapter 8
Describing Chemical Reactions
 A chemical reaction is the process by which one or more
substances are changed into different substances
Reactants → Products
When methane burns in air, it combines with oxygen to
produce carbon dioxide and water.
 Chemical equations represent, with symbols and formulas,
the identities and relative amounts of the reactants and
products in a chemical reaction
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
Describing Chemical Reactions
 To know for certain that a chemical reaction has taken place
requires chemical analysis for proof that one or more
substances has undergone a change in identity
 However, certain easily observed changes usually indicate
that a chemical reaction has occurred
1. Evolution of heat and light
2. Production of a gas
3. Formation of a precipitate
4. Color change
Describing Chemical Reactions
Word equations to chemical equations
Solid ammonium dichromate decomposes when heated to
yield solid chromium (III) oxide and gaseous nitrogen and
water.
(NH4)2Cr2O7(s)
∆
Cr2O3(s) + N2(g) + 4H2O(l)
 The equation must represent know facts
 The equation must contain the correct formulas for the
reactants and products
 The law of conservation of mass must be satisfied
Balancing Chemical Reactions
For each of the following, generate a chemical equation.
 Solid magnesium and aqueous hydrochloric acid react to
form aqueous magnesium chloride and hydrogen gas.
Mg(s) + HCl(aq) → MgCl2(g) + H2(g)
 Aqueous nitric acid reacts with solid calcium hydroxide to
produce aqueous calcium nitrate and water.
HNO3(aq) + Ca(OH)2(s) → Ca(NO3)2(aq) + H2O(l)
Balancing Chemical Reactions
For each of the following, generate a chemical equation.
 Solid aluminum carbide reacts with water to produce
methane gas and solid aluminum hydroxide.
Al4C3(s) + H2O(l) → CH4(g) + Al(OH)3(s)
 Solid sodium combines with chlorine gas to produce solid
sodium chloride.
Na(s) + Cl2(g) → NaCl(s)
Balancing Chemical Reactions
For each of the following, generate a chemical equation.
 When solid copper reacts with aqueous silver nitrate, the
products are copper (II) nitrate and solid silver.
Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2(aq)
 In a blast furnace, the reaction between solid iron (III) oxide
and carbon monoxide gas produces solid iron and carbon
dioxide gas.
Fe2O3(s) + CO(g) → Fe(s) + CO2(g)
Balancing Chemical Reactions
For each of the following, generate a chemical equation.
 When liquid hexane (C6H14) is burned in the presence of
oxygen gas, carbon dioxide and water vapor are produced.
C6H14(g) + O2(g) → CO2(g) + H2O(g)
 Liquid carbon tetrachloride is produced from the reaction of
methane (CH4) with chlorine gas. Hydrogen chloride is a byproduct
CH4(g) + Cl2(g) → CCl4(l) + HCl(g)
Balancing Chemical Reactions
For each of the following, generate a chemical equation.
 Aluminum reacts with oxygen to produce solid aluminum
oxide.
Al(s) + O2(g) → Al2O3(s)
 Phosphoric acid is produced through the reaction of
tetraphosphorous decoxide and water.
P4O10(s) + H2O(l) → H3PO4(aq)
Balancing Chemical Reactions
For each of the following, generate a chemical equation.
 Solid potassium chlorate is heated to produce solid
potassium chloride and oxygen gas.
KClO3(s) → KCl(s) + O2(s)
Balancing Chemical Reactions
Most equations can be balanced by inspection but there are a
few helpful hints that will make it easier.
 Balance the atoms one at a time
 Balance polyatomic ions that appear on both sides as single
units
 Balance atoms that appear alone last
 Check to make sure your final coefficients are in the lowest
whole number ratio possible
Balancing Chemical Reactions
For each of the following, generate a balanced chemical
equation.
 Solid magnesium and aqueous hydrochloric acid react to
form aqueous magnesium chloride and hydrogen gas.
__Mg(s) + __HCl(aq) → __MgCl2(g) + __H2(g)
 Aqueous nitric acid reacts with solid calcium hydroxide to
produce aqueous calcium nitrate and water.
__HNO3(aq) + __Ca(OH)2(s) → __Ca(NO3)2(aq) + __H2O(l)
Balancing Chemical Reactions
For each of the following, generate a balanced chemical
equation.
 Solid aluminum carbide reacts with water to produce
methane gas and solid aluminum hydroxide.
__Al4C3(s) + __H2O(l) → __CH4(g) + __Al(OH)3(s)
 Solid sodium combines with chlorine gas to produce solid
sodium chloride.
__Na(s) + __Cl2(g) → __NaCl(s)
Balancing Chemical Reactions
For each of the following, generate a balanced chemical
equation.
 When solid copper reacts with aqueous silver nitrate, the
products are copper (II) nitrate and solid silver.
__Cu(s) + __AgNO3(aq) → __Ag(s) + __Cu(NO3)2(aq)
 In a blast furnace, the reaction between solid iron (III) oxide
and carbon monoxide gas produces solid iron and carbon
dioxide gas.
__Fe2O3(s) + __CO(g) → __Fe(s) + __CO2(g)
Balancing Chemical Reactions
For each of the following, generate a balanced chemical
equation.
 When liquid hexane (C6H14) is burned in the presence of
oxygen gas, carbon dioxide and water vapor are produced.
__C6H14(l) + __O2(g) → __CO2(g) + __H2O(g)
 Liquid carbon tetrachloride is produced from the reaction of
methane (CH4) with chlorine gas. Hydrogen chloride is a byproduct
__CH4(g) + __Cl2(g) → __CCl4(l) + __HCl(g)
Balancing Chemical Reactions
For each of the following, generate a balanced chemical
equation.
 Aluminum reacts with oxygen to produce solid aluminum
oxide.
__Al(s) + __O2(g) → __Al2O3(s)
 Phosphoric acid is produced through the reaction of
tetraphosphorous decoxide and water.
__P4O10(s) + __H2O(l) → __H3PO4(aq)
Balancing Chemical Reactions
For each of the following, generate a balanced chemical
equation.
 Solid potassium chlorate is heated to produce solid
potassium chloride and oxygen gas.
__KClO3(s) → __KCl(s) + __O2(g)
Types of Chemical Reactions
There are several different ways to categorize chemical
reactions and none are entirely satisfactory. The classification
system described in this chapter is an intro to the five basic
types of reactions:
1. Synthesis
2. Decomposition
3. Combustion
4. Single Replacement
5. Double Replacement
Types of Chemical Reactions
Synthesis
 Two or more substances combine to form a new compound
 A + X → AX
 2Mg(s) + O2(g) → 2MgO(s)
Decomposition
 A single compound undergoes a reaction that produces two
or more simpler substances
 AX → A + X
 2H2O(l) → 2H2(g) + O2(g)
Types of Chemical Reactions
Combustion
 A substance (usually a hydrocarbon) combines with oxygen
to release a large amount of energy in the form of heat and
light
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)
2H2(g) + O2(g) → 2H2O(g)
Water as a Medium for Reactions
Many chemical reactions take place in an
aqueous environment
Water provides a medium in which reacting
species can move around and collide with
each other
Water as a Medium for Reactions
Solid Phase
• Ions are
rigidly held in
place
• No freedom
of movement
H2O
Aqueous Phase
• Ions are
unbound
• Free to move
independently
The Dissolution Process
Ionic compounds break up into their respective
ions in solution
The Dissolution Process
The name of the compound is a direct indicator
of the ions that make it up
The Dissolution Process
 For example NaCl is named sodium chloride
 NaCl(s)
𝐻2𝑂
NaCl(aq) or Na+(aq) + Cl-(aq)
The Dissolution Process
 CaBr2 is named calcium bromide
 CaBr2(s)
𝐻2𝑂
CaBr2(aq) or Ca2+(aq) + 2Br-(aq)
The Dissolution Process
 Na2CO3 is called sodium carbonate
 Na2CO3(s)
𝐻2𝑂
Na2CO3(aq) or 2Na+(aq) + CO32-(aq)
Single Replacement Reactions
One element replaces another
less active element in a
compound
 Mg(s) + H2O(l)
 Mg is more active than H so Mg
replaces one of the Hs in the
compound
Mg(s)+ H2O(l) → Mg(OH)2(aq) + H2(g)
Single Replacement Reactions
One element replaces another
less active element in a
compound
 Au(s) + H2O(l)
Au is less active than H so no
replacement occurs
Au(s) + H2O(l) → no reaction
Single Replacement Reactions
Use Table J to predict whether or not a reaction will occur.
___Ni(s) + ___H2O(l) →
___Au(s) + ___HCl(aq) →
___Br2(l) + ___KI(aq) →
___Mg(s) + ___Co(NO3)2(aq) →
___Ca(s) + ___HCl(aq) →
Double Replacement Reactions
 When solutions are mixed the ions have a
chance to interact with other
 CaBr2(aq) + NaCl(aq)
 Ca2+(aq) + 2Br-(aq) + Na+(aq) + Cl-(aq) → no reaction
Ca2+
BrBr-
Na+
Cl-
Ca2+
BrClNa+
Br-
Double Replacement Reactions
 Na2CO3(s)
 AgNO3(s)
𝐻2𝑂
𝐻2𝑂
Na2CO3(aq) or 2Na+(aq) + CO32-(aq)
AgNO3(aq) or Ag+(aq) + NO3-(aq)
 2Na+(aq) + CO32-(aq) + 2Ag+(aq) + 2NO3-(aq)
↓
Ag2CO3(s) + 2Na+(aq) + 2NO3-(aq)
Na+
Na+
CO3
2-
PRECIPITATE
Na+
Ag+
NO3-
NO3Ag2CO3
Double Replacement Reactions
 2Na+(aq)+ CO32-(aq)+ 2Ag+(aq)+ 2NO3-(aq) → Ag2CO3(s) + 2Na+(aq)+ 2NO3-(aq)
Complete Ionic
 2Ag+(aq)+ CO32-(aq) → Ag2CO3(s)
Net Ionic – eliminates spectator ions
 Na2CO3(aq)+ 2AgNO3(aq) → Ag2CO3(s) + 2NaNO3(aq)
Molecular
Na+
Na+
CO3
2-
Na+
Ag+
NO3-
NO3Ag2CO3
Double Replacement Reactions
Using the solubility guidelines, predict whether or not the
following double replacement reactions will occur. For
those reactions that will proceed, write the products and
balance the resulting chemical equation.
___(NH4)2S(aq) + ___ZnCl2(aq) →
___KNO3(aq) + ___NaCl(aq) →
___Ba(NO3)2(aq) + ___K2SO4(aq) →
___LiF(aq) + ___NH4Cl(aq) →
Double Replacement Reactions
Look for evidence of a chemical reaction
when combining 2 different salt solutions
KOH
KI
Pb(NO3)2
BaCl2
K2SO4
Na3PO4
AgNO3
Double Replacement Reaction
KOH
KOH
KI
Pb(NO3)2
BaCl2
K2SO4
Na3PO4
AgNO3
KI
Pb(NO3)2
BaCl2
K2SO4
Na3PO4
AgNO3